The present invention relates generally to tensioners used with chain drives in automotive timing and power transmission applications. In particular, the present invention is related to a hydraulic chain tensioner system having a pivoting tensioner arm which acts to simultaneously tension two strands of a chain in an engine timing application.
Chain tensioning devices, such as hydraulic tensioners, are used as control devices for power transmission chains as the chain travels between a plurality of sprockets. In an automotive application, the tension of the chain can vary greatly due to the wide variation in the temperature and the linear expansion among the various parts of the engine. Moreover, wear to the chain components during prolonged use can produce a decrease in the tension of the chain. As a result, it is important to impart and maintain a certain degree of tension to the chain to prevent noise, slippage, or unmeshing of the chain with the sprocket teeth. It is especially important in the case of a chain-driven camshaft in an internal combustion engine to prevent the chain from slipping because the camshaft timing can be misaligned by several degrees, possibly rendering the engine inoperative or causing damage.
A hydraulic tensioner as used with a tensioner arm or shoe is shown in Simpson et al., U.S. Pat. No. 5,967,921, which is incorporated herein by reference. Hydraulic chain tensioners typically have a plunger slidably fitted into a chamber and biased outward by a spring to provide tension to the chain. A lever, arm or shoe is often used at the end of the plunger to assist in the tensioning of the chain. The hydraulic pressure from an external source, such as an oil pump or the like, flows into the chamber through passages formed in the housing. The plunger is moved outward against the arm by the combined efforts of the hydraulic pressure and the spring force.
When the plunger tends to move in a reverse direction (inward) away from the chain, typically a check valve is provided to restrict the flow of fluid from the chamber. In such a fashion, the tensioner achieves a so-called no-return function, i.e., movements of the plunger are easy in one direction (outward) but difficult in the reverse direction. In addition, rack and ratchet mechanisms, which are well known in the art are employed to provide a mechanical no-return function.
One example of a chain tensioner which uses a hydraulic tensioner and a pivoted lever to tension a chain is described in Sato et al., U.S. Pat. No. 5,318,482. Sato et al. show a conventional hydraulic tensioner with a plunger pressing a pivoted lever against a chain to impart an appropriate tension to the chain. The tensioner and single shoe arm of Sato et al. has limitations, however, in the amount of chain slack it can take up during the life of the chain. In addition, the single shoe arm of Sato et al. has limitations in its ability to absorb and damp cyclic vibrations in the chain during operation.
Conventional prior art tensioners which tension only one strand of chain, i.e., a single length of chain between two sprockets, in an engine timing application with long center distances between the sprockets have a common weakness. During operation of the engine, wear on the various chain parts causes the chain to lengthen. Taking up the resulting slack on one side of an engine timing system and not the other can cause the timing of the camshaft to change relative to the crankshaft. In some engine timing chain applications, the large center distances cause both sides of the chain span between sprockets to slacken as the chain wears and extends in length.
To address the above conventional problems the present invention includes an actuator in the form of a conventional hydraulic tensioner in combination with a pivoting tensioner arm. The tensioner arm may include either two shoes or two pair of shoes. In combination, the shoes operate on separate strands of a common chain. This potentially provides approximately double the operating take-up for a given range of tensioner operation as compared to a conventional hydraulic tensioner acting upon a single arm with an end pivot that acts on one chain strand. When used to tension separate strands of a single chain, vibrations which occur in one strand of chain tend to be cancelled when the energy of those vibrations are transferred to or combined with those in another strand through the pivoting tensioner. Further, when taking up chain slack in an engine timing application, the present invention minimizes the chance for changes in the timing between the crankshaft and the camshaft as the chain wears and slackens on both sides of the chain span between the sprockets.
The present invention provides a chain tensioner system including an actuator, which may be a conventional hydraulic tensioner, in conjunction with a pivoting tensioner arm assembly that contacts both lengths or strands of the span of chain between a pair of sprockets.
The chain tensioner system of the present invention includes a hydraulic actuator as described above and a pivoting tensioner arm. The tensioner arm is located between a pair of rotating sprockets which are drivingly interconnected by a chain. The chain has at least two separate strands, spans or lengths that are the portions extending between the sprockets. The portion between the sprockets where the chain leaves the cam sprocket and enters the crankshaft sprocket is typically the tight side as a result of the tension imposed on the chain to drive the camshaft sprocket. The portion between the sprockets where the chain leaves the crankshaft sprocket and enters the camshaft sprocket is typically the slack side of the chain on account of the absence of driving of the camshaft along that strand. However, in systems with large center distances between the sprockets, both sides evidence some slack.
The tensioner arm includes a bracket or a main body portion which is shaped essentially like an xe2x80x9cIxe2x80x9d in which both ends have been flattened. Near the center of the body is a pivot bore. The pivot bore is a hole with a cylindrical sleeve or bushing through which a pivot pin, shaft or bolt is inserted and about which the arm may rotate. The pivot pin is attached to an engine or mounting surface. The main body portion comprises two leg portions that extend from the pivot point out to the chain strands.
In a first embodiment of the tensioner arm, the top end of the main body, at the end of one leg, includes a first tab. The tab extends along nearly the entire length of the top end of the leg and is bent perpendicular to the body. The tab holds a shoe which has a face which contacts an outside of a first free strand of chain. A second tab is formed on the bottom or second end of the body in a similar manner to the first tab. A second shoe is disposed on the bottom or second tab opposite the top or first shoe. The second shoe has a face which contacts an outside of a second strand of chain.
The actuator in this embodiment is a spring biased plunger which acts upon an outside surface of the tensioner arm, i.e., one of the tabs on the body, to impart a rotational force upon the arm and tension both strands of the chain simultaneously. Actuation of the plunger against one tab causes rotation of the entire arm or body about the pivot point. The inward motion of the first tab against one strand causes tension to be applied to the strand. Similarly, the inward motion of the second strand causes tension to be applied to that strand. The actuator may be a spring biased plunger, hydraulic tensioner, mechanical tensioner or any suitable mechanism which is capable of providing sufficient force and travel to act on the tensioner arm and provide an adjustment in tension of the chain.
In a second embodiment of the present invention, the tensioner arm is also located within the span of chain between two sprockets or on the inside of the two chain strands. The tensioner arm includes a main body portion which is essentially xe2x80x9cIxe2x80x9d shaped. A first end or upper end of the body is near the camshaft sprocket and a second end or lower end is near the crank sprocket. The main body portion includes a pair of nearly parallel sides formed along each of the two legs. A first side is adjacent the slack side of the chain and a second side is adjacent the tight side of the chain.
The main body portion of the tensioner arm includes a pair of tabs at the first or upper end of the main body portion along one leg and a pair of tabs at the second or lower end of the main body portion along the second leg. Each tab carries a shoe. Both shoes on the first or left side of the body are oriented about the slack strand of the chain. The upper left shoe is located outside the slack strand of the chain near the camshaft. The lower left shoe is located inside the slack strand of the chain near the crankshaft. The upper right shoe is located inside the tight strand of the chain near the camshaft. The lower right shoe is located outside the tight strand of the chain near the crankshaft.
In this way, a left shoe on the first end of the body contacts the outside of the slack strand of chain and a right shoe on the same end of the body contacts the inside of the tight strand near the camshaft sprocket. Similarly, a left shoe on the second or lower end of the body contacts the inside of the slack strand of chain and a right shoe on the same end of the body contacts the outside of the tight strand near the crankshaft sprocket. In other words, each strand of the chain has a pair of shoes, one shoe at one end of the body contacting the outside of the strand and the other shoe at the other end of the body contacting the inside of the strand.
In operation, the piston or plunger of the tensioner, which may be hydraulically actuated, directs a force to an outside shoe or main body portion which causes the tensioner arm to pivot. Rotation of the arm causes each chain strand to be tensioned in a similar manner. Rotation of the tensioner arm causes the upper and lower shoe on the left side to contact the slack chain strand and the upper and lower right shoes to contact the tight chain strand.
In particular, the upper left shoe imparts tension to the slack chain strand by displacing the slack chain strand path toward the chain centerline. The lower left shoe imparts tension to the slack chain strand by displacing the slack chain strand path away from the chain centerline. The same direction of rotation of the arm causes the upper right shoe to impart tension to the tight chain strand by displacing the tight chain strand path away from the chain centerline. The lower right shoe imparts tension to the tight chain strand by displacing the tight chain strand path toward the chain centerline.
For a further understanding of the present invention and the objects thereof, attention is directed to the drawing and the following brief description thereof, to the detailed description of the preferred embodiment of the invention and to the appended claims.